Other person: "Why is X.500 so special? Why is no-one else doing this?"
Me: "Get your favourite book on database technology and look up 'Hierarchical databases'".
[Time passes]
Other person: "I looked in several books. Many didn't mention it at all, and one had a half-page historical note saying it's something that was obsoleted by better technology more than two decades ago".
Me: "Exactly".